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A multimeter is an indispensable test equipment for troubleshooting and measuring electrical circuits. It is a handheld device that can measure voltage, current, and resistance in electrical systems:
● Voltage: The voltage function allows you to measure both alternating current (AC) and direct current (DC) voltage. The DC voltage comes out of batteries, where the current flows in only one direction, while the AC voltage comes from wall outlets, where the current periodically reverses direction.
● Current: The current function lets you measure amperage in AC and DC circuits. Current is the amount of charge flowing through a circuit.
As we've already seen, a multimeter is one of the most basic and useful tools for any technician working with circuit boards. It allows you to troubleshoot issues by checking voltage, continuity, and resistance across components. Following the proper steps is critical to test a circuit board and identify potential problems thoroughly.
If voltage levels are too high or low, resistances read as shorts or opens, or component tests reveal abnormalities, you've likely found the source of a problem. Note the location and readings on the board for reference during repairs. Continuing tracing up and down the signal chain can help narrow things down further. Once all issues are identified, the circuit board is fully diagnosed and ready for repairs.
Here is a video guide about how to test a circuit board with a multimeter.
Flying probe testing is like in-circuit testing, only without physical contact. Movable probes are elevated slightly above the board on a gantry system. High-frequency signals are transmitted between the probes and circuit traces. Reflected signals are analyzed by the machine to determine if electrical properties meet specifications. It's helpful in testing bare boards before assembly and doesn't pose a risk of contacting sensitive components.
A high-resolution camera examines the board through a microscope under different lighting conditions. It captures images and compares them to reference images of a known good board with pattern recognition software. Any deviations in solder joints, placement of components, or missing or excess solder are automatically detected. AOI ensures assembly defects won't cause reliability issues.
A trained technician examines the board under magnification with good lighting. Although it's the least sophisticated method, the human eye can still spot subtle defects missed by automated inspection, such as dents, scratches, bridging, icicles, and component placement issues. Visual inspection remains a crucial final check after other testing is completed.
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